Fire doors are provided in buildings to present passage and spread of fires from one portion of the building to other portions. Various types of fire doors are provided to close different kinds of openings generally found in buildings, such as double swing doors. Typical double swing doors comprises an active door and an inactive door.
Flush bolt mechanisms are used on what is normally termed the inactive door of a pair of double swing doors. The flush bolt mechanism includes the male member, i.e. generally a trigger, of a door latch combination with the female bolt receiving plate or strike positioned if the opposing active door. While a major portion of the flush bolt mechanism is mounted on what is termed the free side of the inactive door, an additional latch bolt and guide mechanism are connected to the flush bolt mechanism by a long linkage to provide a locking bolt that is normally received in a second strike positioned in the lentil of the doorway.
Flush bolt mechanisms are shown and described at U.S. Pat. Nos. 4,005,886, 4,445,717, and 5,076,620. However, with a double set of swing doors, a space between opposing door jambs, in the walls in which the doors are mounted, has to be provided for clearance between the jamb and the pivoting side of each of the opposing doors plus clearance between the free sides of the opposing doors. Heretofore, in order to adjust the doors and the door locking mechanisms thereon for a double set of swing doors, additional shimming has to be provided for the hinges in the doorjambs. As the clearances in a double set of swing doors are greater than that found in a single swing door, means for adjusting a door bolt mechanism to accommodate varying clearances between the double swing doors and the door sash has to be developed and employed.
Referring to FIGS. 1-2, U.S. Pat. No. 6,409,231 discloses a conventional flush bolt mechanism 1 comprises an elongated rod type linkage 2, a slide guide 3, a link 5, first and second coil springs 5 and 6, a latch bolt 7, a trigger member 8, a plunger (not labeled) and a bell crank 9. The latch bolt 7 is connected to the main mechanism by the elongated rod type linkage 2. The elongated rod type linkage 2 extends slidably through the slide guide 3. A lower portion of the elongated rod type linkage 2 is enclosed by the first coil spring 5. The link 5 is enclosed by the second coil spring 6. One end of the link 5 is fixed to the slide guide 3, and the other end thereof is fixed to the bell crank 9.
In operation, the trigger member 8 is pushed back into the plunger as an active door is closed, the bell crank 9 moves to push the slide guide 30 upwardly through the link 5 to move the elongated rod type linkage 2 upwardly and make sure the latch bolt 7 is inserted into a strike in a door lentil (not shown). The horizontal movement of the trigger member 8 is transferred to the vertical movement of the link 5 by means of the bell crank 9. This tends to give rise to abrasive wear of the bell crank 9 after repeated use. The service life of such flush bolt mechanism is thus undesirably reduced.
It is therefore greatly desired to provide a new and improved flush bolt mechanism suitable for double swing doors.